The invention relates to an electric arc furnace in which solids and/or gases are blown by means of lances into the furnace chamber in order to produce a foamed slag for the reduction or alloying-up of the melt or for the recycling of substances.
It is common when operating electric arc furnaces to blow during the melting, mainly, however, during the warming and deoxidation period, during which no solid iron but only the liquid melt exists, carbon and/or oxygen through lances into the electric arc furnace. The lances are moved by means of lance manipulators, whereby the lances blow through the slag door the solids or gases into the furnace. On the one hand, additional energy is supplied to the process through this, on the other hand, the slag is foamed up by the reaction of the blown-in carbon with the iron oxide existing in the slag while forming carbon monoxide and carbon dioxide. The advantages of producing such a foamed slag are essentially the improved energy transfer from the tip of the graphite electrodes into the melt and the reduced refractory attack through the enveloping of the arc with the slag. This causes also a drop in the specific energy and electrode consumption. Through the reduction of the slag the production of the metallic iron in the form of liquid steel is improved, and the required time for the entire melt is at the same time reduced.
Moreover it is possible to blow through the lances besides carbon carriers, mainly lime, filter dust, fine parts from the iron sponge production and prepared sludge into the electric arc furnace.
The disadvantage of these conventional methods is that by using the lance manipulators in the area of the slag door a considerable amount of space is needed, and moreover the lance""s must be replaced often. Due to the blowing in of the additives in the area of the slag door, the adjoining area preferably produces a high slag, whereas more or less slag exists in the remaining furnace areas. This has significant disadvantages. In particular, the slag foaming takes place only in one area so that sufficient slag is missing in the area opposite the slag door. This is mainly noticeable in electric arc furnaces which have an eccentric bay tapping feature. When in addition filter dust or other solids to be recycled are supplied through the lances, then the amount of the added solids is limited because the addition is concentrated at an area in the furnace area following the slag door. This easily results in formations of solid agglomerates which are difficult to melt. In addition because of the uneven slag distribution the know-how of the operating personnel is important most of all in deciding as to when and in what amount the additives must be blown into the electric arc furnace.
The basic purpose of the invention is to provide an electric arc furnace and a method for the operation of the electric arc furnace, in particular for the production of a foamed slag, so that not only a significantly quicker build-up of the slag with a more even distribution in the surface and in the height of the furnace chamber of the electric arc furnace is achieved, but that it is also possible to add additives in greater amounts than was the case up to now, and the electric arc furnace has a greater durability.
This purpose is attained according to the invention by the lances being guided through the wall of the electric arc furnace and being inserted into the wall of the furnace by at least one lance being associated with each electrode, whereby the lances are arranged approximately uniformly distributed over the periphery of the furnace, the inclination of the lances and thus the injection angle being chosen such that these define an angle of approximately 30 to 80xc2x0 with respect to the flow direction of the molten bath, and an angle of approximately 10 to 30xc2x0 with respect to the horizontal.
By arranging the lances in the wall of the furnace, it is possible to carry out the feeding of carbon, gases and other solids in a specific manner into the furnace chamber, distributed over its surface, so that a slag produced over the furnace chamber is created with essentially the same height. This does not only significantly improve the protection of the masonry of the furnace but the efficiency of the supplied energy is improved. The lances are hereby advantageously aligned in such a manner that the injection surface lies in flow direction of the melt in front of the respective electrodes. The formation of a foamed slag evenly distributed over the furnace chamber is thus supported in addition by the flow of the melt.
The parts of the lances, which are inserted into the furnace wall, and which can consist of steel or also of copper, are water-cooled, which significantly improves their durability. The port of the lances lies thereby no higher than 200 mm above the surface of the molten bath.
An iventively designed electric arc furnace is advantageously during the melting phase additionally loaded with oxygen and/or natural gas through the lances. Carbon and/or oxygen is then during the warming phase alternately blown through the lances into the furnace in order to produce in this manner a sufficient foamed slag. It is hereby also possible to blow besides carbon also lime, filter dust, iron-containing dust, prepared sludge and cinder, alloys and/or mixtures of these substances through the lances into the furnace. The substance flow in the feed pipe to the lances is hereby individually controlled so that the locally varying amount of additives, which are blown distributed over the bath surface into the furnace, contributes additionally to the control of the amount and thus the distribution of the foamed slag.
Pressurized air is advantageously used to supply the solids, which pressurized air flows also during standstill times, when no solids are moved through the lances, through said lances, and thus besides an additional cooling are also used to avoid a plugging up of the lances.